1. Field of the Invention
The present invention relates generally to serial bus technology and more particularly, to power control and communication in universal serial bus technology.
2. Description of the Related Art
Personal computer systems have attained widespread use. These personal computer systems now provide computing power to many segments of today's society. A personal computer system can usually be defined as a desktop or portable microcomputer that includes a system unit having a system processor with associated volatile and non-volatile memory, a display monitor, a keyboard, a hard disk storage device or other type of storage media such as a floppy disk drive or a compact disk read only memory (CD ROM) drive. One of the distinguishing characteristics of these systems is the use of a system board or motherboard to electrically connect these components together. These personal computer systems are information handling systems which are designed primarily to give independent computing power to a single user or group of users and are inexpensively priced for purchase by individuals or small businesses.
FIG. 1, which is labeled "prior art", represents a typical computer system 2 including a host computer 4 holding a processor and memory (not shown). The peripherals shown connected to the system 2 include a mouse 10, a keyboard 8, a telephone 16 and an external disk drive 14. Each of these peripherals is connected to the system 2 through a number of different interfaces and connectors, with each peripheral having a separate socket and connector.
Many personal computers hold multiple external peripheral interfaces for attaching peripheral devices. For example, a printer and a modem typically require an RS-232 interface, a peripheral disk drive typically requires a Small Computer System Interface (SCSI), a mouse or a keyboard typically requires a third interface. Thus, multiple interfaces become necessary for a personal computer to operate. With each type of interface comes a different type of connector and a different power requirement.
Alternatively, an external hub could be used to serve as a central location for connecting peripheral devices to the computer using the same type of connector. A hub compatible with the Universal Serial Bus (USB) standard offers a single type of connector. One problem with using a USB hub, however, is that there are several power modes supported by the specification, so-called "bus-powered" and so-called "self-powered" modes.
Therefore, it can be appreciated that there is a need for a universal hub that has the advantages of both "bus-powered" hubs and "self-powered" hubs, but in a single hub that has the capability of controlled switching between power modes.